Cathode active material and method of manufacturing the same, cathode including the same, and lithium secondary battery

Abstract

To provide a cathode active material which includes a lithium nickel-based complex oxide and which can achieve long-life characteristics by inhibiting structural deterioration and crack generation from being caused by charge and discharge, while achieving a high capacity, a cathode, and a lithium secondary battery.SOLUTION: A cathode active material, which assumes a particle form including a lithium nickel-based complex oxide, includes a nickel reduction layer which is positioned on a particle surface and which contains nickel having an oxidation number smaller than 3+. The nickel reduction layer exists with a thickness of 10 nm or less in a center direction from the particle surface. The cathode active material, a method of manufacturing the same, a cathode including the same, and a lithium secondary battery are provided.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a positive electrode active material, a method for producing the same, a positive electrode containing the same, and a lithium secondary battery.

Background Art

[0002] Lithium secondary batteries having a high energy density and being easy to carry are mainly used as driving power sources for mobile information terminals such as mobile phones, notebook computers, and smartphones. Recently, research has been actively conducted on using lithium secondary batteries having a high energy density as driving power sources or power storage power sources for hybrid automobiles and electric vehicles.

[0003] In order to realize a lithium secondary battery suitable for such applications, various positive electrode active materials have been studied. Among them, lithium nickel-based oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, lithium cobalt oxides, etc. are mainly used as positive electrode active materials. High-nickel-based positive electrode active materials having a nickel content of about 80 mol% or more can achieve a high energy density, and thus have been actively developed recently. However, there are limitations accompanied by various problems such as structural deterioration due to charge and discharge, surface side reactions with the electrolyte, and deterioration due to particle cracks. Therefore, development of a positive electrode active material that can achieve a high energy density and long-life characteristics is required.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Provided are a positive electrode active material containing a lithium nickel-based composite oxide, a positive electrode, and a lithium secondary battery, which can suppress structural deterioration and crack generation due to charge and discharge while realizing a high capacity, and can realize long-life characteristics.

Means for Solving the Problems

[0005] In one embodiment, there is provided a positive electrode active material in the form of particles containing a lithium nickel-based composite oxide, which includes a nickel reduction layer located on the surface of the particles and containing nickel with an oxidation number less than 3+, and the nickel reduction layer exists with a thickness of 10 nm or less from the surface of the particles toward the center direction.

[0006] In another embodiment, there is provided a method for manufacturing a positive electrode active material, which includes mixing a nickel-based composite hydroxide and a lithium raw material and performing a primary firing, pulverizing the primary fired product, washing it with washing water, drying the washed primary fired product, and then performing a secondary firing, and the weight ratio of the primary fired product pulverized in the washing step to the washing water satisfies 1:0.5 to 1:0.9.

[0007] In another embodiment, there is provided a positive electrode for a lithium secondary battery including the above-described positive electrode active material.

[0008] In another embodiment, there is provided a lithium secondary battery including the positive electrode, a negative electrode, and an electrolyte.

Advantages of the Invention

[0009] The positive electrode active material according to one embodiment can realize long-life characteristics by suppressing structural deterioration and crack generation due to repeated charge and discharge, side reactions with the electrolyte, etc., while realizing high capacity.

Brief Description of the Drawings

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Best Mode for Carrying Out the Invention

[0011] Hereinafter, specific embodiments will be described in detail so that those having ordinary knowledge in the technical field can easily implement them. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein.

[0012] The terms used herein are merely used to explain exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0013] Here, "these combinations" means a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, a reaction product, etc.

[0014] Terms such as "comprising", "including" or "having" herein are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and it should be understood that they do not preclude the presence or addition of one or more other features, numbers, steps, components, or combinations thereof in advance.

[0015] In the drawings, the thickness is enlarged to clearly show a plurality of layers and regions, and the same reference numerals are given to similar parts throughout the specification. When a part such as a layer, a film, a region, a plate, etc. is "on" another part, this includes not only the case where it is "directly on" another part, but also the case where there are other parts in between. Conversely, when a part is "directly on" another part, it means that there are no other parts in between.

[0016] Also, here, the "layer" includes not only the shape formed on the entire surface when observed in a plan view, but also the shape formed on a part of the surface.

[0017] The average particle size can be measured by methods widely known to those skilled in the art. For example, it can be measured with a particle size analyzer, or it can also be measured from a transmission electron microscope image or a scanning electron microscope image. As another method, it can be measured using the dynamic light scattering method, data analysis can be performed to count the number of particles for each particle size range, and then the average particle size value can be obtained by calculation based on this. Unless otherwise defined, the average particle size may mean the diameter (D 50 ) of the particles with a cumulative volume of 50% by volume in the particle size distribution. Also, unless otherwise defined, the average particle size is obtained by measuring the sizes (diameter or major axis length) of more than 20 randomly selected particles in a scanning electron microscope image to obtain a particle size distribution, and taking the diameter (D 50 ) of the particles with a cumulative volume of 50% by volume from the particle size distribution as the average particle size.

[0018] Here, "or" is not interpreted in an exclusive sense. For example, "A or B" is interpreted to include A, B, A + B, etc.

[0019] "Metal" is interpreted as a concept including common metals, transition metals, and metalloids (semi-metals).

[0020] Positive electrode active material In one embodiment, it is a positive electrode active material in the form of particles containing a lithium nickel-based composite oxide, including a nickel reduction layer located on the surface of the particles and containing nickel with an oxidation number less than 3+, and the nickel reduction layer provides a positive electrode active material existing with a thickness of 10 nm or less from the surface of the particles toward the center.

[0021] The content of nickel with respect to 100 mol% of the total metal excluding lithium in the lithium nickel-based composite oxide may be 80 mol% or more, for example, 85 mol% or more, 90 mol% or more, 91 mol% or more, 94 mol% or more, or 99 mol% or less.

[0022] The lithium nickel-based composite oxide may be represented, for example, by the following Chemical Formula 1. [Chemical Formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0023] In the chemical formula 1, 0.9 ≦ a1 ≦ 1.2, 0.8 ≦ x1 < 1, 0 < y1 ≦ 0.2, 0 ≦ z1 ≦ 0.2, 0.9 ≦ x1 + y1 + z1 ≦ 1.1, and 0 ≦ b1 ≦ 0.1, and M 1 and M 2 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

[0024] In the chemical formula 1, 0.85 ≦ x1 < 1, 0 < y1 ≦ 0.15, and 0 ≦ z1 ≦ 0.15, or 0.9 ≦ x1 < 1, 0 < y1 ≦ 0.1, and 0 ≦ z1 ≦ 0.1 may be satisfied.

[0025] The lithium nickel-based composite oxide may be represented by the following chemical formula 2 or chemical formula 3 as specific examples. [Chemical formula 2] Li a2 Ni x2 Co y2 M 3 z2 O 2-b2 X b2

[0026] In the chemical formula 2, 0.9 ≦ a2 ≦ 1.2, 0.8 ≦ x2 < 1, 0 < y2 ≦ 0.2, 0 ≦ z2 ≦ 0.2, 0.9 ≦ x2 + y2 + z2 ≦ 1.1, and 0 ≦ b2 ≦ 0.1, and M 3 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is F, P, S, or a combination thereof.

[0027] In the chemical formula 2, 0.9 ≦ x2 ≦ 0.99, 0.01 ≦ y2 ≦ 0.1, and 0 ≦ z2 ≦ 0.1 can be satisfied.

[0028] [Chemical formula 3] Li a3 Ni x3 Co y3 M 4 z3 M 5 w3 O 2-b3 X b3

[0029] In the chemical formula 3, 0.9 ≦ a3 ≦ 1.2, 0.8 ≦ x3 ≦ 0.98, 0.01 ≦ y3 ≦ 0.19, 0.01 ≦ z3 ≦ 0.19, 0 ≦ w3 ≦ 0.19, 0.9 ≦ x3 + y3 + z3 + w3 ≦ 1.1, and 0 ≦ b3 ≦ 0.1, where M 4 is Al, Mn, or a combination thereof, and M 5 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is F, P, S, or a combination thereof.

[0030] In the chemical formula 3, 0.9 ≦ x3 ≦ 0.98, 0.01 ≦ y3 ≦ 0.09, 0.01 ≦ z3 ≦ 0.09, and 0 ≦ w3 ≦ 0.09 can be satisfied.

[0031] In such a high-nickel cathode active material, excessive residual lithium is generated on the particle surface during the synthesis process, so a water washing process is required. Through the water washing process, Li present on the surface of the cathode active material particles 2 CO 3Ideally, only lithium compounds such as LiOH are removed, but depending on the degree and conditions of water washing, there is a risk of removing even the active lithium inside the cathode active material. When lithium in the cathode active material structure is removed in this way, not only does the reversible capacity decrease, but crystal structure changes and phase transitions may occur, leading to performance degradation. For example, while lithium elutes, the form such as lithium-nickel-oxide changes to the form such as nickel-oxide, and for example, NiO may be formed. Therefore, a kind of reduction reaction occurs in which the oxidation number of Ni decreases from 3+ to 2+. Since compounds such as NiO are not converted back to lithium-containing compounds, not only does the reversible capacity decrease, but side reactions between the surface of the cathode active material particles and the electrolyte may be promoted, resulting in a problem of overall performance degradation. Thus, the part where the oxidation number of nickel becomes lower than 3+ on the surface of the cathode active material particles can be referred to as a nickel reduction layer, and for example, a low oxidation layer or a disordering layer.

[0032] In one embodiment, by appropriately adjusting the water washing process to suppress the thickness of the nickel reduction layer to 10 nm or less, a cathode active material is proposed that can suppress the deterioration of the cathode active material paper due to charge and discharge and improve the life characteristics of the lithium secondary battery.

[0033] The thickness of the nickel reduction layer can be, for example, 7 nm or less, and can be 1 nm to 7 nm, 1 nm to 5 nm, or 2 nm to 4 nm. The thickness of the nickel reduction layer can be measured by TEM-EELS analysis of the cross-section of the cathode active material particles. For example, for the cross-section of the cathode active material particles, in the TEM image, EELS analysis is performed from the surface of the particles toward the inside, and the part where the peak near 855 eV in the EELS analysis graph shifts to the left can be recognized as the part where the oxidation state of nickel changes to less than 3+, and this part can be defined as the nickel reduction layer. The nickel reduction layer according to one embodiment is observed in a thickness range of 10 nm or less from the surface of the particles toward the inside.

[0034] The nickel reduction layer may contain NiO, and the composition inside the particles excluding the nickel reduction layer, for example, the composition of Chemical Formula 1 and the composition such as NiO may be mixed. Thereby, the oxidation number of nickel in the nickel reduction layer can be 2+ or more and less than 3+, for example, 2+ or more and 2.5+ or less.

[0035] The oxidation number of nickel in the particles excluding the nickel reduction layer can be 3+.

[0036] The particles can be in the form of secondary particles formed by aggregation of a plurality of primary particles or in the form of single particles.

[0037] The average particle diameter (D 50 ) can be 0.5 μm to 20 μm, or 1 μm to 18 μm. For example, when the particles are in the form of secondary particles, the average particle diameter (D 50 ) of the secondary particles can be 3 μm to 20 μm, 5 μm to 18 μm, or 8 μm to 15 μm. When the particles are in the form of single particles, the average particle diameter (D 50 ) of the single particles can be 0.5 μm to 8 μm, or 1 μm to 5 μm. The average particle diameter can be obtained, for example, by measuring the particle sizes (particle diameter, major axis diameter, or length of the major axis) of any 20 or more particles in a scanning electron microscope image to obtain a particle size distribution, and calculating the size (D 50 ) of the particle with a cumulative volume of 50% by volume.

[0038] Here, a single particle means that it exists independently without having a grain boundary inside the particle and consists of one particle, and can mean a single particle, a monolith structure or a single body structure or non-aggregated particles that exist as an independent phase in which the particles do not aggregate with each other morphologically, and can be, for example, a single crystal. The single particles may exist alone, or the single particles may be gathered together. For example, 2 to 10 single particles may be gathered and in contact with each other.

[0039] On the one hand, when the particles are in the form of secondary particles, at least a part of the primary particles forming the secondary particles may be arranged radially. Hereinafter, the radial form will be described.

[0040] At least a part of the primary particles forming the secondary particles can have a plate shape. In the plate structure, the maximum length on the widest surface can be defined as the length of the major axis (a), the maximum length of the surface that is substantially perpendicular to the widest surface can be defined as the thickness (t), and the thickness is shorter than the length of the major axis. The direction in which the length of the major axis is included is the plane direction, and the direction in which the thickness is defined is the thickness direction. In one embodiment, the radially arranged structure means that the thickness direction of the primary particles is arranged perpendicular to the direction from the center to the surface of the secondary particles or arranged at an angle of ±5° with the vertical direction.

[0041] When at least a part of the primary particles has a radially arranged structure, the secondary particles can have relatively more lithium diffusion channels between the primary particles on the surface side, and many crystal planes capable of lithium transfer to the outside are exposed, improving the lithium diffusion degree and enabling the securing of high initial efficiency and capacity. Also, the open pores exposed on the surface can be directed toward the center of the secondary particles to promote the diffusion of lithium. And the radially arranged primary particles enable uniform contraction and expansion of the secondary particles during the desorption and / or insertion of lithium. The presence of pores on the (001) direction side, which is the direction in which the particles expand during lithium desorption, allows such pores to exert a buffering effect on contraction and expansion. Also, the size and arrangement of the primary particles reduce the probability of cracks occurring during the contraction and expansion of the secondary particles, and the pores existing inside the secondary particles additionally relieve the volume change, reducing the cracks generated between the primary particles during charge and discharge, improving the life characteristics of the lithium secondary battery, and reducing the resistance increase phenomenon.

[0042] For example, the secondary particles may include an interior containing an irregular porous structure and a region surrounding the interior and containing a radial arrangement structure on the outside. That is, the primary particles arranged inside may be arranged without regularity, unlike the primary particles arranged outside. The radial arrangement structure means that at least a part of the primary particles are arranged radially. The pore size and porosity inside are larger than the pore size and porosity outside and can be irregular.

[0043] When the secondary particles have an irregular porous structure inside, there is an effect of reducing the diffusion distance of lithium ions to the inside. On the other hand, since the primary particles are arranged radially on the outside, it becomes easy for lithium ions to be inserted into the surface. And when the size of the primary particles is small, it becomes easy to secure a lithium transfer path between the crystal grains. And when the size of the primary particles is small, the pores between the primary particles relieve the volume change that occurs during charge and discharge, and the stress due to the volume change during charge and discharge is minimized. Such a positive electrode active material can reduce the resistance of the lithium secondary battery and improve the capacity characteristics and life characteristics.

[0044] On the other hand, the positive electrode active material according to one embodiment may have a ratio of the peak intensity at 250°C to the peak intensity at 220°C of less than 20 in differential scanning calorimetry (DSC) analysis, for example, 19 or less, or 15 or less.

[0045] Also, in DSC analysis, it can be characterized by no peak appearing in the range of 170°C to 210°C, for example, around about 190°C. Further, in DSC analysis, the heat generation amount in the range of 170°C to 210°C (for example, 190°C) can be 30 J / g or less, or 1 to 20 J / g. When the positive electrode active material satisfies such DSC analysis results, there is little structural deterioration due to charge and discharge, crack generation is suppressed, and excellent life characteristics can be realized.

[0046] Method for producing positive electrode active material In one embodiment, there is provided a method for manufacturing a positive electrode active material including: (i) mixing a nickel-based composite hydroxide and a lithium raw material and performing a first firing; (ii) pulverizing the first fired product and then washing it with washing water; and (iii) drying the washed first fired product and then performing a second firing. Here, the weight ratio of the first fired product pulverized in the washing step to the washing water satisfies 1:0.5 to 1:0.9, and the weight ratio may be, for example, 1:0.6 to 1:0.8, or 1:0.7 to 1:0.9.

[0047] In the case of a high-nickel positive electrode active material, excessive residual lithium is generated on the surface, and thus it is necessary to perform a water washing operation during the synthesis process. At this time, it is common to wash using 1 part by weight or more of washing water with respect to 1 part by weight of the positive electrode active material. However, in one embodiment, the amount of washing water is adjusted to 0.9 part by weight or less with respect to 1 part by weight of the positive electrode active material, and an attempt is made to relieve washing by self-restraining the use of additional washing water. As a result, the thickness of the nickel reduction layer on the surface of the positive electrode active material particles is reduced to the level of several nanometers, structural degradation of the positive electrode active material due to repeated charge and discharge is suppressed, and the life characteristics of the lithium secondary battery can be improved.

[0048] The content of nickel in the nickel-based composite hydroxide with respect to 100 mol% of the total metal may be 80 mol% or more, and may be, for example, 85 mol% or more, 90 mol% or more, 91 mol% or more, 94 mol% or more, or 99 mol% or less.

[0049] The nickel-based composite hydroxide may be represented by, for example, Chemical Formula 11. [Chemical Formula 11] Ni x11 M 11 y11 M 12 z11 (OH) 2

[0050] In Chemical Formula 11, 0.8 ≦ x11 < 1, 0 < y11 ≦ 0.2, 0 ≦ z11 ≦ 0.2, 0.9 ≦ x11 + y11 + z11 ≦ 1.1, and M 11 and M 12They are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr.

[0051] In Chemical Formula 11, 0.85 ≦ x11 < 1, 0 < y11 ≦ 0.15, and 0 ≦ z11 ≦ 0.15, or 0.9 ≦ x11 < 1, 0 < y11 ≦ 0.1, and 0 ≦ z11 ≦ 0.1 may be satisfied.

[0052] The molar ratio of the metal of the nickel-based composite hydroxide to lithium of the lithium raw material can be, for example, 1:0.9 to 1:1.2.

[0053] The first firing can be carried out in an oxygen atmosphere, for example, in a temperature range of 700 °C to 950 °C, or 730 °C to 900 °C, or 750 °C to 890 °C, and can be carried out for 2 hours to 20 hours, or 4 hours to 18 hours.

[0054] The second firing can be carried out, for example, in an oxygen atmosphere in a temperature range of 600 °C to 820 °C, 650 °C to 800 °C, or 670 °C to 750 °C for 2 hours to 20 hours, or 3 hours to 17 hours. Also, the second heat treatment temperature may be lower than the first heat treatment temperature, and the second heat treatment time may be the same as or shorter than the first heat treatment time.

[0055] Positive electrode In one embodiment, a positive electrode for a lithium secondary battery including the above-described positive electrode active material is provided. For example, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and the positive electrode active material layer can include the above-described positive electrode active material. The positive electrode active material layer can further include other types of positive electrode active materials in addition to the above-described positive electrode active material, and can selectively further include a binder, a conductive agent, or a combination thereof.

[0056] Binder The binder plays a role in enabling the positive electrode active material particles to adhere well to each other and also enabling the positive electrode active material to adhere well to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, and the like.

[0057] Conductive agent The conductive agent is used to impart conductivity to the electrode, and in the configured battery, any electron conductive material that does not cause a chemical change can be used. Examples of the conductive agent include carbon-based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based substances in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0058] The contents of the binder and the conductive agent can each be 0.5 wt% to 5 wt% with respect to 100 wt% of the positive electrode active material layer.

[0059] As the positive electrode current collector, Al can be used, but it is not limited thereto.

[0060] Lithium secondary battery In one embodiment, a lithium secondary battery including the positive electrode, negative electrode, and electrolyte described above is provided. As an example, the lithium secondary battery can include a positive electrode, a negative electrode, a separator positioned between the positive electrode and the negative electrode, and an electrolyte solution.

[0061] Lithium secondary batteries can be classified into cylindrical, square, pouch, coin, etc. according to their form. FIGS. 1 to 4 are schematic views showing a lithium secondary battery according to an embodiment. FIG. 1 shows a cylindrical form, FIG. 2 shows a square form, and FIGS. 3 and 4 can be of a pouch type battery form. Referring to FIGS. 1 to 4, the lithium secondary battery 100 can include an electrode assembly 40 with a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is incorporated. The positive electrode 10, negative electrode 20, and separator 30 may be impregnated with an electrolytic solution (not shown). The lithium secondary battery 100 can include a sealing member 60 for sealing the case 50 as shown in FIG. 1. Also, in FIG. 2, the lithium secondary battery 100 can include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 3 and 4, the lithium secondary battery 100 can include electrode tabs 70, that is, a positive electrode tab 71 and a negative electrode tab 72, which serve as an electrical path for guiding the current formed by the electrode assembly 40 to the outside.

[0062] Negative electrode The negative electrode can include a current collector and a negative electrode active material layer located on this current collector. The negative electrode active material layer can include a negative electrode active material and can further include a binder, a conductive agent, or a combination thereof.

[0063] Negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / desorbing lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping with lithium, or a transition metal oxide.

[0064] Examples of the material capable of reversibly inserting / desorbing the lithium ions include carbon-based negative electrode active materials, which can include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, fired coke, etc.

[0065] As the alloy of the lithium metal, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0066] As the substance capable of doping and undoping lithium, an Si-based negative electrode active material or an Sn-based negative electrode active material can be used. As the Si-based negative electrode active material, silicon, a silicon-carbon composite, SiOx (0 < x < 2), an Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, for example, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or a combination thereof can be used. As the Sn-based negative electrode active material, Sn, SnO 2 , an Sn alloy, or a combination thereof can be used.

[0067] The silicon-carbon composite can be a composite of silicon and amorphous carbon. The average particle size (D 50 ) of the silicon-carbon composite particles can be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite can be in a form in which silicon particles and amorphous carbon are coated on the surface of the silicon particles. For example, it can include secondary particles (cores) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon is also located between the primary silicon particles, and for example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed in an amorphous carbon matrix.

[0068] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0069] When the silicon-carbon composite contains silicon and amorphous carbon, the content of silicon may be 10% to 50% by weight based on 100% by weight of the silicon-carbon composite, and the content of amorphous carbon may be 50% to 90% by weight. When the composite contains silicon, amorphous carbon, and crystalline carbon, the content of silicon may be 10% to 50% by weight based on 100% by weight of the silicon-carbon composite, the content of crystalline carbon may be 10% to 70% by weight, and the content of amorphous carbon may be 20% to 40% by weight.

[0070] Also, the thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. The average particle diameter (D 50 ) of the silicon particles (primary particles) may be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles may exist alone as silicon, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon may be represented by SiO x (0 < x < 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation may be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle diameter (D 50 ) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0071] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material and the carbon-based negative electrode active material are used in combination, the mixing ratio may be 1:99 to 90:10 by weight.

[0072] Binder The binder plays a role in enabling the negative electrode active material particles to adhere well to each other and enabling the negative electrode active material to adhere well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0073] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0074] Examples of the aqueous binder may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0075] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity can be further included. As this cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof can be mixed and used. As the alkali metal, Na, K, or Li can be used.

[0076] The dry binder is a polymer substance capable of being fibrillated, and can be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0077] Conductive agent The conductive agent is used to impart conductivity to the electrode, and in the battery being configured, any electron - conductive material that does not cause a chemical change can be used. Specific examples include carbon - based substances such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal - based substances in the form of metal powder or metal fiber containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0078] The content of the negative electrode active material can be 95% by weight to 99.5% by weight based on 100% by weight of the negative electrode active material layer, and the content of the binder can be 0.5% by weight to 5% by weight based on 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer can contain 90% by weight to 99% by weight of the negative electrode active material, 0.5% by weight to 5% by weight of the binder, and 0.5% by weight to 5% by weight of the conductive agent.

[0079] Current collector The negative electrode current collector can contain, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof, and can be in the form of a foil, sheet, or foam. The thickness of the negative electrode current collector can be, for example, 1 μm to 20 μm, can be 5 μm to 15 μm, or can be 7 μm to 10 μm.

[0080] Electrolyte The electrolyte for a lithium secondary battery can be, for example, an electrolytic solution, which can contain a non-aqueous organic solvent and a lithium salt.

[0081] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. The non-aqueous organic solvent can be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0082] As the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used. As the ester-based solvent, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. can be used. As the ether-based solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. can be used. Also, as the ketone-based solvent, cyclohexanone, etc. can be used. As the alcohol-based solvent, ethyl alcohol, isopropyl alcohol, etc. can be used, and as the aprotic solvent, nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and can contain a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane, 1,4-dioxolane; sulfolane-based compounds, etc. can be used.

[0083] The non-aqueous organic solvent can be used alone or in a mixture of two or more. When used in a mixture of two or more, the mixing ratio can be appropriately adjusted according to the desired battery performance, which can be widely understood by those skilled in the art.

[0084] When using a carbonate solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0085] The non-aqueous organic solvent can further contain an aromatic hydrocarbon-based organic solvent. For example, the carbonate solvent and the aromatic hydrocarbon-based organic solvent can be mixed and used in a volume ratio of 1:1 to 30:1.

[0086] The electrolyte can further contain vinyl ethyl carbonate, vinylene carbonate or an ethylene carbonate-based compound to improve the battery life.

[0087] Typical examples of the ethylene carbonate-based compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate and the like.

[0088] The lithium salt is dissolved in an organic solvent, acts as a source of lithium ions in the battery to enable the operation of a basic lithium secondary battery, and plays a role in promoting the movement of lithium ions between the positive electrode and the negative electrode. Typical examples of the lithium salt include LiPF 6 、LiBF 4 、LiSbF 6 、LiAsF 6 、LiClO 4 、LiAlO 2 、LiAlCl 4 、LiPO 2 F 2 、LiCl、LiI、LiN(SO 3 C2 F 5 ) 2 、 Li(FSO 2 ) 2 N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC 4 F 9 SO 3 、 LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 )(where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), lithium bis(oxalate)borate (LiBOB), and can include one or more selected therefrom.

[0089] The concentration of the lithium salt is preferably used in the range of 0.1 M to 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has appropriate ionic conductivity and viscosity, so it can exhibit excellent performance and lithium ions can move effectively.

[0090] Separator Depending on the type of lithium secondary battery, a separator can also be present between the positive electrode and the negative electrode. As such a separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof can be used, and it goes without saying that a mixed multilayer film such as a two-layer separator of polyethylene / polypropylene, a three-layer separator of polyethylene / polypropylene / polyethylene, or a three-layer separator of polypropylene / polyethylene / polypropylene can be used.

[0091] The separator can include a porous substrate and a coating layer located on one or both sides of the porous substrate and containing an organic substance, an inorganic substance, or a combination thereof.

[0092] The porous substrate can be a polymer selected from any one of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyether imide, polyamide imide, polybenzimidazole, polyether sulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a polymer film formed of a copolymer or mixture of two or more of these.

[0093] The porous substrate can have a thickness of about 1 μm to 40 μm, for example, a thickness of 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0094] The organic substance can include a (meth)acrylic copolymer containing a first structural unit derived from (meth)acrylamide and a second structural unit including at least one of a structural unit derived from (meth)acrylic acid or (meth)acrylate and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0095] The inorganic substance is Al 2 O 3 SiO 2 TiO 2 SnO 2 CeO 2 MgO, NiO, CaO, GaO, ZnO, ZrO 2 Y 2 O 3 SrTiO 3 BaTiO 3 Mg(OH) 2、 boehmite and inorganic particles selected from combinations thereof, but not limited thereto. The average particle size (D 50) can be from 1 nm to 2000 nm, for example, it can be from 100 nm to 1000 nm, or from 100 nm to 700 nm.

[0096] The organic matter and the inorganic matter can be present as a mixture in one coating layer, or can be present in a form in which a coating layer containing the organic matter and a coating layer containing the inorganic matter are laminated.

[0097] The thickness of each of the coating layers can be from 0.5 μm to 20 μm, for example, it can be from 1 μm to 10 μm, or from 1 μm to 5 μm.

[0098] Hereinafter, examples and comparative examples of the present invention will be described. The following examples are merely illustrative of the present invention, and the present invention is not limited to the following examples.

[0099] Example 1 1. Production of positive electrode active material (1) Production of first lithium nickel-based composite oxide Through the coprecipitation method described later, the first nickel-based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH) 2 ), which is a precursor of the first positive electrode active material, was synthesized. Nickel sulfate (NiSO 4 ·6H 2 O), cobalt sulfate (CoSO 4 ·7H 2 O) and sodium aluminum sulfate (NaAl(SO 4 ) 2 ·12H 2 O) are dissolved in distilled water as a solvent so as to have a molar ratio of 94.5:4:1.5 to prepare a metal raw material mixed solution. Also, ammonia water (NH 4 OH) and sodium hydroxide (NaOH) as a precipitating agent are prepared for the formation of the complex compound.

[0100] [First stage: 2.5 kW / m 3 , NH 4 OH 0.40 M, pH 10.5 - 11.5, reaction time 6 hours] First, aqueous ammonia with a concentration of 0.40 M was put into the reactor. With a stirring power of 2.5 kW / m 3 , while maintaining the reaction temperature at 50°C, the reaction was started while feeding the metal raw material mixed solution and the complexing agent (NH 4 OH) at rates of 85 ml / min and 10 ml / min, respectively. The reaction was carried out over 6 hours while adding NaOH to maintain the pH. As a result of the reaction, it was confirmed that the average size of the obtained core particles was in the range of about 6.5 μm to 7.5 μm, and the second stage was carried out as follows.

[0101] [Second stage: 2.0 kW / m 3 , NH 4 OH 0.45 M, pH 10.5 - 11.5, reaction time 18 hours] While maintaining the reaction temperature at 50°C, the feeding rates of the metal raw material mixed solution and the complexing agent were changed to 85 ml / min and 12 ml / min, respectively, so that the concentration of the complexing agent became 0.45 M. The reaction was carried out for 18 hours while adding NaOH to maintain the pH. At this time, the stirring power was lowered to 2.0 kW / m 3 lower than that in the first stage to proceed with the reaction. By carrying out such a reaction, it was confirmed that the average size of the product particles including the core and the intermediate layer was 13.5 μm to 14 μm, and the third stage was carried out as follows.

[0102] [Third stage: 1.5 kW / m 3 , NH 4 OH 0.45 M, pH 10.5 - 11.5, reaction time 14 hours] While maintaining the reaction temperature at 50°C, the feeding rates of the metal raw material mixed solution and the complexing agent and the concentration of the complexing agent were made the same as those in the second stage. The reaction was carried out for 14 hours while adding NaOH to maintain the pH. At this time, the stirring power was lowered to 1.5 kW / m 3 lower than that in the second stage to proceed with the reaction.

[0103] [Post - process] After washing the resultant, it was dried with hot air at about 150°C for 24 hours to obtain the first nickel - based composite hydroxide (Ni 0.945 Co 0.04 Al 0.015 (OH)2 ) was obtained.

[0104] [Primary firing] The first nickel-based composite hydroxide and LiOH were mixed so as to satisfy a molar ratio of Li / (Ni + Co + Al) = 1.01, charged into a firing furnace, and subjected to primary firing at 820 °C for 8 hours in an oxygen atmosphere to produce a composite oxide (primary fired product). Thereafter, the composite oxide was pulverized through an air current impact pulverizer so that the average particle size (D 50 ) became about 13 μm. A first lithium nickel-based composite oxide having a composition of Li 1.01 Ni 0.945 Co 0.04 Al 0.015 O 2 and in which at least a part of the primary particles are arranged radially in the form of secondary particles was produced.

[0105] (2) Production of second lithium nickel-based composite oxide The second nickel-based composite hydroxide, which is a precursor of the second positive electrode active material, was synthesized through a coprecipitation method (Ni 0.94 Co 0.04 Al 0.01 Mn 0.01 (OH) 2 ). As metal raw materials, nickel sulfate (NiSO 4 ·6H 2 O), cobalt sulfate (CoSO 4 ·7H 2 O), sodium aluminum sulfate (NaAl(SO 4 ) 2 ·12H 2 O) and manganese sulfate (MnSO 4 ·H 2 O) were dissolved in distilled water as a solvent so as to have a molar ratio of 94:4:1:1 to prepare a mixed solution. The subsequent synthesis is the same as the production of the first nickel-based composite hydroxide.

[0106] The second nickel-based composite hydroxide produced by the above method and lithium hydroxide were mixed at a molar ratio of 1:1 and heat-treated at 870 °C in an oxygen atmosphere. The average particle size (D 50) was pulverized so that it became about 2 μm to obtain a single-particle form lithium nickel-based composite oxide (LiNi 0.94 Co 0.04 Al 0.1 Mn 0.01 O 2 ) which is a second lithium nickel-based composite oxide.

[0107] (3) Production of mixed positive electrode active material The first lithium nickel-based composite oxide and the second lithium nickel-based composite oxide were mixed at a weight ratio of 8:2, and this mixture and washing water (distilled water) were mixed at a weight ratio of 1:0.9 for washing. Then, the washing water was separated, and after the product was dried at 180 °C, it was secondarily fired at 750 °C for 8 hours to produce a final positive electrode active material in which the first positive electrode active material and the second positive electrode active material were mixed.

[0108] 2. Production of lithium secondary battery 98.5% by weight of the produced positive electrode active material, 1.0% by weight of a polyvinylidene fluoride binder, and 0.5% by weight of a carbon nanotube conductive agent were mixed to produce a positive electrode active material layer slurry, which was coated on an aluminum foil current collector and dried and rolled to produce a positive electrode.

[0109] 97.5% by weight of a graphite negative electrode active material, 1.5% by weight of carboxymethyl cellulose, and 1% by weight of styrene-butadiene rubber were mixed in an aqueous solvent to produce a negative electrode active material layer slurry. The negative electrode active material layer slurry was coated on a copper foil current collector and dried and rolled to produce a negative electrode.

[0110] Using a polytetrafluoroethylene separator, a lithium secondary battery was manufactured in a usual method using an electrolytic solution in which 1M LiPF 6 was dissolved in a solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 3:7.

[0111] Comparative Example 1 In the washing step of manufacturing the positive electrode active material, after mixing the pulverized primary fired product and washing water at a weight ratio of 1:0.9, an additional 0.6 parts by weight of washing water is further added, and washing is performed under the condition that the weight ratio of the pulverized primary fired product to the washing water becomes 1:1.5. Otherwise, the positive electrode active material and the lithium secondary battery were manufactured in substantially the same manner as in Example 1.

[0112] Evaluation Example 1: STEM and EELS analysis The thickness of the nickel reduction layer can be specifically measured by the following method. (i) Obtain a TEM image of the cross-section of the positive electrode active material particles cut by FIB, (ii) magnify the vicinity of the surface of the particles in the cross-sectional TEM image to obtain a STEM image, (iii) perform EELS analysis in the direction inward from the surface of the particles in the STEM image to obtain EELS data by depth, (iv) find a graph in which the peak near 855 eV in the EELS data is shifted to the left, and confirm how deep these graphs appear from the surface of the particles, and the depth can be defined as the thickness of the nickel reduction layer. FIG. 5 is a TEM image of a cross-section of the first positive electrode active material, which is a radial secondary particle form in the positive electrode active material manufactured in Comparative Example 1, cut by a focused ion beam (FIB). FIG. 6 is a STEM image taken by magnifying the portion indicated by the square in FIG. 5. EELS analysis was performed in the direction indicated by the arrow in FIG. 6, and the results are shown in FIG. 7. It can be said that the portion where the peak near 855 eV in FIG. 7 is shifted to the left is the position where the oxidation number of nickel has changed to less than 3+. This is shown by reflecting the thickness on the TEM image of the cross-section of the positive electrode active material of Comparative Example 1 in FIG. 8. Referring to FIG. 8, it is confirmed that the thickness of the nickel reduction layer where the oxidation number of nickel has changed to less than 3+ is at about 25 nm level.

[0113] FIG. 9 is a TEM image of a cross-section of the first positive electrode active material, which is a radial secondary particle form in the positive electrode active material particles manufactured in Example 1, cut by FIB, and FIG. 10 is a STEM image taken by magnifying the portion with an arrow in FIG. 9. EELS analysis was performed in the depth direction in FIG. 10, and the results are shown in FIG. 11. Similarly, it can be said that the portion where the peak near 855 eV is shifted to the left in FIG. 11 is the position where the oxidation number of nickel changed to less than 3+. This is displayed by reflecting the thickness on the TEM image of the cross-section of the positive electrode active material of Example 1 in FIG. 12. Referring to FIG. 12, in the case of Example 1, it is confirmed that the thickness of the nickel reduction layer where the oxidation number of nickel changed to less than 3+ is at about 3 nm level.

[0114] In the case of Comparative Example 1, the thickness of the nickel reduction layer is at 25 nm level, while in the case of Example 1, it can be confirmed that the thickness is further reduced to 7 nm or less level.

[0115] Evaluation Example 2: DSC analysis DSC analysis was performed on the positive electrode active materials manufactured in Example 1 and Comparative Example 1, and the results are shown in FIG. 13. The reason why there are three graphs for Example 1 is that all the experimental results for the positive electrode active material of Example 1 are reflected. Referring to FIG. 13, in the case of Comparative Example 1, the first peak appears at around 190 °C, while in the case of Example 1, it can be seen that no peak appears at that temperature. The DSC analysis was measured using a differential scanning calorimeter (SENSYS·Evo; SETARAM). Specifically, 15 mg of the anode filled at 4.45 V (vs. Li / Li + ) was collected, 20 μl of the electrolyte was added to prepare an evaluation cell, and then the temperature was raised to 400 °C at a rate of 10 °C / min, and the heat flow rate due to temperature was measured.

[0116] Also, the calorific value at the first peak near 190 °C was calculated through DSC analysis and shown in Table 1 below.

[0117]

Table 1

[0118] Referring to Table 1, in the case of Example 1, it can be seen that the calorific value near 190°C is 19 J / g or less, which is lower than that of Comparative Example 1.

[0119] Evaluation Example 3: Evaluation of life characteristics The lithium secondary batteries manufactured in Example 1 and Comparative Example 1 were charged at a constant current of 0.2 C to 4.45 V at 25°C and then at a constant voltage to 0.05 C, and then discharged at 0.2 C to 3.0 V to perform initial charge and discharge. Next, a cycle of charging at 1.0 C and discharging at 1.0 C in the voltage range of 3.0 V to 4.45 V at 45°C was repeated 75 times. The discharge capacity graph according to the number of cycles is shown in FIG. 14. Referring to FIG. 14, it can be seen that the life characteristics of Example 1 were more improved than those of Comparative Example 1.

[0120] FIG. 15 is an SEM image of the cross-section of the positive electrode active material of Comparative Example 1 taken after 75 cycles. FIG. 16 is an enlarged image of the large particles in the secondary particle form in FIG. 15, and FIG. 17 is an enlarged image of the small particles in the single particle form in FIG. 15. Referring to FIGS. 15 to 17, in the case of Comparative Example 1, it can be seen that many cracks occurred in both the large particles and the small particles after 75 cycles, and fine pores were generated and the structural deterioration progressed.

[0121] FIG. 18 is an SEM image of the cross-section of the positive electrode active material of Example 1 taken after 75 cycles. Referring to FIG. 18, it can be seen that almost no cracks or fine pores were observed in both the large particles and the small particles compared with Comparative Example 1, and the structural deterioration was effectively suppressed, and thus it can be seen that the life characteristics of Example 1 were improved.

[0122] Although the preferred embodiments have been described in detail above, the scope of the rights of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concepts defined in the claims also belong to the scope of the rights of the present invention.

Explanation of Reference Numerals

[0123] 100: Lithium secondary battery 10: Positive electrode 11: Positive electrode lead tab 12: Positive electrode terminal 20: Negative electrode 21: Negative electrode lead tab 22: Negative electrode terminal 30: Separator 40: Electrode assembly 50: Case 60: Sealing member 70: Electrode tab 71: Positive electrode tab 72: Negative electrode tab

Claims

1. A particulate positive electrode active material containing a lithium nickel-based composite oxide, a nickel reduction layer located on the surface of the particle and containing nickel with an oxidation number less than 3+; The nickel reduction layer is present in a thickness of 10 nm or less from the surface toward the center of the particle.

2. 2. The positive electrode active material according to claim 1, wherein the lithium-nickel-based composite oxide has a nickel content of 80 mol % or more relative to 100 mol % of all metals excluding lithium.

3. The positive electrode active material according to claim 1 , wherein the lithium nickel-based composite oxide is represented by Chemical Formula 1: [Chemical formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 (In the above formula 1, 0.9≦a1≦1.2, 0.8≦x1<1, 0<y1≦0.2, 0≦z1≦0.2, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1; M 1 and M. 2 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

4. The positive electrode active material according to claim 1, wherein the nickel reduction layer has a thickness of 1 nm to 7 nm.

5. The positive electrode active material according to claim 1 , wherein the oxidation number of nickel in the nickel reduction layer is 2+ or more and 2.5+ or less.

6. The positive electrode active material according to claim 1 , wherein the nickel oxidation number in the particles excluding the nickel reduction layer is 3+.

7. The positive electrode active material of claim 1 , wherein the nickel reduction layer comprises NiO.

8. The positive electrode active material according to claim 1 , wherein the particles are in the form of secondary particles formed by agglomeration of a plurality of primary particles or in the form of single particles.

9. The average particle size of the particles (D 50 2. The positive electrode active material according to claim 1, wherein the thickness of the first electrode is 0.5 μm to 20 μm.

10. 2. The positive electrode active material of claim 1, wherein in a differential scanning calorimetry analysis, the ratio of the peak intensity at 250° C. to the peak intensity at 220° C. is less than 20.

11. 2. The positive electrode active material according to claim 1, which does not exhibit a peak in the range of 170° C. to 210° C. in differential scanning calorimetry analysis.

12. 2. The positive electrode active material according to claim 1, which has a calorific value of 30 J / g or less in a temperature range of 170° C. to 210° C. in a differential scanning calorimetry analysis.

13. A nickel-based composite hydroxide and a lithium raw material are mixed and primarily baked; After crushing the primary fired product, wash it with washing water. The washed first fired product is dried and then fired for a second time, In the washing step, a weight ratio of the pulverized primary calcined material to the washing water is 1:0.5 to 1:0.

9.

14. The method for producing a positive electrode active material according to claim 13, wherein a weight ratio of the pulverized primary fired product and the washing water satisfies 1:0.7 to 1:0.

9.

15. The method for producing a positive electrode active material according to claim 13, wherein the nickel content in the nickel-based composite hydroxide is 80% by weight to 99% by weight relative to 100 mol% of the total metal.

16. The method for producing a positive electrode active material according to claim 13 , wherein the nickel-based composite hydroxide is represented by chemical formula 11. [Chemical formula 11] Ni x11 M 11 y11 M 12 z11 (OH) 2 (In the above formula 11, 0.8≦x11<1, 0<y11≦0.2, 0≦z11≦0.2, and 0.9≦x11+y11+z11≦1.1; M 11 and M. 12 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Zn, and Zr.

17. The method for producing a positive electrode active material according to claim 13, wherein a molar ratio of the metal of the nickel-based composite hydroxide to the lithium of the lithium raw material is 1:0.9 to 1:1.

2.

18. The primary firing is carried out at a temperature range of 700°C to 950°C, The method for producing a positive electrode active material according to claim 13, wherein the secondary firing is performed at a temperature range of 600° C. to 820° C.

19. A positive electrode for a lithium secondary battery comprising the positive electrode active material according to any one of claims 1 to 12.

20. The positive electrode according to claim 19 . a negative electrode, and A lithium secondary battery containing an electrolyte.

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